The invention concerns an assembly element and a timepiece comprising the same.
The invention concerns more specifically an assembly element made in a plate of brittle material such as silicon, particularly for a timepiece, including an aperture provided for the axial insertion of an arbour, the inner wall of the aperture including elastic structures which are etched in the plate and which each comprise at least one support surface for gripping or squeezing the arbour radially in order to secure the assembly element relative to the arbour, wherein each elastic structure includes a first rectilinear elastic strip which extends along a tangential direction relative to the arbour, the support surface being arranged on the inner face of the first elastic strip.
Generally, in timepieces, the assembly elements such as the timepiece hands and the toothed wheels are secured by being driven into their rotating arbour, i.e. a hollow cylinder is forced onto a pin whose diameter is slightly greater than the inner diameter of the cylinder. The elastic and plastic properties of the material employed, generally a metal, are used for driving in said elements. For components made of a brittle material such as silicon, which does not have a usable plastic range, it is not possible to drive a hollow cylinder onto a conventional rotating arbour like those used in mechanical watchmaking, with a diameter tolerance of the order of +/−5 microns.
Moreover, the solution for securing an assembly element such as a hand must provide sufficient force to hold the element in place in the event of shocks. The force necessary for a conventional timepiece hand is, for example, of the order of one Newton.
In order to overcome these problems, it has already been proposed to make, in an assembly element such as a silicon balance spring collet, flexible strip shaped elastic structures arranged on the periphery of the aperture, so as to secure the collet onto an arbour by a driving in type arrangement, using the elastic deformation of the strips to grip the arbour and retain the collet on the arbour. An example of this type of securing method is disclosed in particular in EP Patent No. 1 655 642.